چكيده فارسي :
Gallic Acid (3,4,5–trihydroxybenzoic acid) (GA) is one of the main natural phenolic components.
It is extensively used in tanning, ink dyes, manufacturing of paper, food industry, and drug
trimethoprim in the pharmaceutical industry [1, 2]. Rapid and accurate detection of GA is of great
interest to analytical chemistry because it has not only strong anti-mutagenic, anti-carcinogenic,
and anti-oxidant activities but also potential health effects which have been found recently [3]. In
past years, various methods have been applied to determine GA, such as flow injection analysis
[4, 5], resonance light scattering [6], thin–layer chromatography [7], reversed phase highperformance
liquid chromatography [8], and electrochemical method [9,10]. With regard to the
conducted surveys, no MIP-based chemical sensor has been presented so far for determination of
GA. However, MIP has been used to separate GA from aqueous samples. In the present study, a
sensitive electrode is developed to determine GA in very low concentrations. MIP, containing
recognition sites for GA, is synthesized by electropolymerization of aniline on carbon ceramic
electrode in present of GA. For optimization of separation and determination of GA in solutions,
operational parameters include pH solution, pre-concentration time of nanosensor in GA solution
and solution temperature was chosen and optimized via central composite design. Using Design–
Expert 8.0.2 software, a complete CCD matrix include 20 experiments was designed. The
optimal conditions for determination of GA nanosensor were solution pH= 3.62, accumulation
time=45 min and 45 °C as solution temperature. In order to confirmation of improvement the
nanosensor performance due to creation an molecular imprinted membrane (MIM) on carbon
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ceramic electrode (CCE) in determination of GA, DPV of four different electrode such as CCE,
multiwall carbon nanotube modified CCE (MWCNT/CCE), electropolymerized MWCNT/CCE
in absence of GA (ENIM) and in presence of GA (EMIM) was measured based on these optimum
conditions. The mentioned electrodes were separately immersed into a 1.0 mM GA solution with
the pH of 3.62 at 45 ˚C for 60.0 min until GA accumulated on the electrodes. After accumulation
of GA molecules on the electrodes, they were washed with a water-ethanol (50% v–v) solution
and displaced to a phosphate buffer solution with the pH of 7.0. Their DPVs are depicted in Fig
1. As it can be seen, there is no significant reduction current for GA on CCE (curve a) and
ENIM/MWCNT/CCE (curve c). Indeed, CCE and ENIM/MWCNT/CCE have no capability for
trapping and accumulating of GA. On the other hand, by comparing DPVs of CCE (curve a) and
MWCNT/CCE (curve b), it can be conclude that cathodic peak current is increased due to the
presence of MWCNT. It seems that a possible reason for the increase of current is the presence of
MWCNT in the electrode structure; MWCNT has a larger surface area and higher conductivity
than graphite. However, EMIM/MWCNT/CCE (curve d) is considerably indicate the current for
reduction of GA. Thus, the prepared electrode is able to trap GA molecules. Under optimal
experimental conditions, DPVs of EMIM/MWCNT/CCE was recorded to estimate the lower
limit of detection and the linear range of GA. As expected, the reduction peak current increased
upon the increase of GA concentration. Fig 2 clearly indicates that the plot of the reduction peak
current against the GA concentration was linear in the range of 10–500 μM. According to the
method mentioned in Skoog et al. (1998), the lower detection limit, Cm, was calculated 6.5 μM
by using the equation Cm=3sbl/m, where sbl is the standard deviation of the blank response and m
is the slope of the calibration plot (0.006 μA μM). The average voltammetric peak current and the
precision estimated in terms of the coefficient of variation for repeated measurements (n = 15) of
6.5 μM GA at the EMIM/MWCNT/CCE were 0.295 ± 0.007 μA and 2.4 %, respectively.
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Fig 1. Differential pulse voltammogram analysis of electrodes a) bare CCE, b) MWCNT/CCE, c)
ENIM/MWCNT/CCE, and d) EMIM/MWCNT/CCE incubated in 1.0 mM GA solution for 60 min at 45 °C.
Fig 2. Differential pulse voltammograms of EMIM/MWCNT/CCE in a 0.1 M phosphate-buffered solution (pH
7.0) containing different concentrations of GA. Insets show the plots of the electrocatalytic peak current as a
function of GA concentration in the range of 10-500 μM.
